RFC 2581, the April 1999 Proposed Standard on TCP Congestion Control, says the following: ``IW, the initial value of cwnd, MUST be less than or equal to 2*SMSS bytes and MUST NOT be more than 2 segments.''
Allman, M., Floyd, S., and Partridge, C., Increasing
TCP's Initial Window, RFC 2414, Experimental, September 1998.
This
is the document proposing an increase in TCP's permitted initial window.
Poduri, K., and Nichols, K., Simulation
Studies of Increased Initial TCP Window Size, RFC 2415, Experimental,
September 1998.
These simulations model both long-lived TCP connections
(file transfers) and short-lived web-browsing style connections. Simulation
scripts: tar file, compressed tar file.
Additional files for modeling HTTP 1.1 (tar file).
Shepard, T., and Partridge, C., When TCP
Starts Up With Four Packets Into Only Three Buffers . RFC 2415,
Experimental, September 1998.
This paper explores TCP's behavior in a
configuration with a 9600 bps modem and only three packet buffers before the
modem. The simulations in this report show that a four-packet initial window
does not degrade the performance of a long-lived TCP connection.
The proposal from the internet draft has been implemented in the ns simulator. The test suite for this (at the moment, this test suite only includes tests for one-way TCP) can be run with the command "./test-all-tcp-init-win" in the directory "tcl/test".
Floyd, S., a talk on Increasing TCP's Initial Window (postscript, pdf). 40th IETF
Meeting - TCP Implementations WG. December, 1997. Washington DC.
This talk
shows that current TCP implementations routinely send bursts of three and
(perhaps less routinely) four back-to-back packets.
Return to [ Sally Floyd].
Last modified: September 1998